This invention relates to web-moving apparatus and in particular to an improved paper feed system for impact and other printers.
It is desirable in a printer paper feed system to have the capability of feeding various types of paper including rolls, tractor fan fold and single sheets. It is also desirable that such systems have a "short tear-off" capability, i.e., the ability to separate individual sheets of fan fold paper with minimum waste. In conventional tractor drive systems, the paper must be passed through the tractor before tear-off can occur, thus wasting a portion of the form material.
Other prior art systems have attempted to solve this problem, for example, by pushing the paper through a fixed platen, by affixing pin wheels directly on the platen, or by driving a roller platen and a tractor at the same speed.
Pushing the paper through a fixed gap in front of a flat platen works well on some forms, but other forms are not rigid enough to push. This configuration also places the paper in a relatively loose condition near the exit opening of the feed system causing the printer to be very noisy. Further, it is usually difficult to load the paper because the tractors are placed very low in the machine, and these systems are either dedicated to friction drive with fixed pins, or to adjustable tractor drives with no single sheet or roll capability.
Affixing pin wheels directly on the platen alleviates the tear-off problem, however, only one width of paper form can be used and the paper is difficult to load. Other prior art systems which drive the roller platen and tractors together have no way of removing slack between them.